It has previously been proposed to use switching regulator power supplies in hard disk drives, as shown for example in U.S. Pat. No. 4,839,754, granted Jun. 13, 1989; inventors: Bipin V. Gami and Ericson Dunstan, and assigned to the assignee of this invention.
In the field of hard disk drives, the 51/4-inch disk systems have standard over-all dimensions including a height of 3.25 inches (82.6 mm), a width of 5.75 inches (146 mm), and a depth of 8.00 inches (203 mm). Environmental standards have also been established, with the operating temperature extending from 5.degree. C. to 50.degree. C., and the non-operating or storage temperature extending from -40.degree. C. to +65.degree. C.
It has been customary to operate the disk drives so that the speed of rotation of the disks is 3600 rpm, which means that the disks make one revolution in 16.67 milliseconds. For such systems, the average latency time or time to access a sector of digital data is approximately 8.33 milliseconds, or one-half the time for one revolution. Several years ago, the average time for changing tracks on a hard disk drive was about 32 milliseconds, and this has now been reduced to about 12.5 milliseconds, with improved technological developments.
Now, in order to reduce the latency time, certain hard disk drive motor speeds are being increased from 3600 rpm to 5400 rpm, thereby reducing the average time to access a sector from about 8.33 milliseconds to about 5.56 milliseconds.
With increased speed, however, the drive power requirements have increased, as the required drive power increases exponentially with increased speed. In this regard, some manufacturers have been forced to provide heat sinks or cooling fins which extend beyond the dimensional limitations for hard disk drives as set forth hereinabove.
In the motor control circuit of U.S. Pat. No. 4,839,754 the switching regulator power supply, a p-channel Field Effect Transistor (FET), was employed to convert power from the 12 volt supply level to a lower voltage to power the 3600 rpm motor, with much greater efficiency than is obtained with conventional linear power regulators. However, the p-channel FET has a resistance of about 0.3 ohms, and with the circuit parameters of a 5400 rpm hard disk drive motor, the resistance of this p-channel FET increases the circuit power dissipation to undesirably high levels.
Accordingly, a principal object of the present invention is to reduce the power requirements of the drive circuit for a hard disk drive having a high speed motor, such as the 5400 rpm motors.